Process for protecting natural rubber against deterioration by oxidation and composition formed therefrom



PROCESS FOR PROTECTING NATURAL RUBBER AGAINST DETERIORATION BY OXIDATION AND COMPOSITION FORMED THEREFROM' Boris Nicholas Leyland and Ronald Lee'Stafford, Manchester, England, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain 7 Y No Drawing. Application December 22, 1955 7 Serial No. 554,613

Claims priority, application Great Britain December 31, 1954 21 Claims. or. 260-752) This invention relates to rubber antioxidant mixtures and theirapplicationto natural rubber in order to protect the rubber against deterioration by oxidation,'both before and after vulcanisation, especially in the presence of copper or manganese.

According to the present invention we provide a process for protecting natural rubber against deteriora-' tion by oxidation,'especially in, the presence [of copper or manganese, which comprises incorporating into the rubber, at any suitable stage before curing, at least one mercaptoarimidazole and at least one phenol containing atleast one tertiary alkyl or alkylcycloalkyl radical having from 4 to 8 carbon atoms.

The mercaptoarimidazole may be used as such or in the form of its metal salt, for example its zinc, calcium or magnesium salt. The preferred mercaptoarimidazole is Z-mercaptobenzimidazole but others may beused, for example 2:2-dibenzimidazyl disulphide.

We are aware that it has already been proposed to use mixtures of antioxidants generally with mercaptoarimidazoles in order to enhance the antioxidant effect. However it has not hitherto been observed that any special effect with respect to oxidation in the presence of copper or manganese is obtained and it has not been proposed to use mixtures of the phenols of our invention with mercaptoarimidazoles. We have discovered that such mixtures have an unexpected, outstanding effect on the oxidation of natural rubber in the presence of copper or manganese and our present invention is based upon this discovery.

Phenols that can be used in the process of this invention include those described in'UK. specifications Nos. 677,584, 719,101, 728,291, 723,838, 732,928 and 749,450; they may be, for example, bis(2-hydroxy-3-tert.-butyl-5- methylphenyl)-methane, bisl2-hydroxy-3-(u-methylcyclohexyl) methylphenyl] methane, bis(2 hydroxy 3 tert. butyl 5 ethylphenyl) methane, 2:2 di hydroxy 3 tert. octyl 3' methyl 5:51 dimethyl diphenylmethane, 2:2 dihydroxy 3 tert. butyl 3 (a methylcyclohexyl) 5:5 dimethyldiphenylmethane, 2:2 dyhydroxy 3:3 di tert. butyl -'5:5' dimethyl diphenyl ale: butane, 2:6 dimethyl 4 tert. butyl phenol, 2:6 di di tert. butyl 4 methylphenol, 2-

(m methylcyclohexyl) 4:6 dimethylphenol or the metal salts thereof.

The proportion of mercaptoarimidazole to be used in the process of this invention may be from about 50% to about 200% of the weight of the phenol; preferably the proportion is about 100%. The amount of the combined agents used in the rubberis conveniently from.

0.5%, to 4.0% of the weight of the rubber hydrocarbon.

The'efficacy of the process of this invention may be even further enhanced by the further incorporation into the'rubber of a copper-sequestering agent, for example ethylene diamine tetracetic acid or a metal salt thereof,

ll disalicylal alkylenediamines, 8-hydroxyquinoline or paminophenol. However the phenolic antioxidants 'de scribed and their'mixtures with the mercaptoarimidazole's give compoundswhich do not stain on exposure to light and when it is desired ,to retain this advantagethe copper sequestering agents S-hydroxyquinoline and p-aminophenol should not be used. Suitable proportions of these agents are from 3% to 10% of the total weight of the copper-inhibiting system. If. it. is .desired to retain .the advantage of a non-staining'compoundthen the l pper limit of 10% should not be exceeded in thecase of the disalicylal alkylenediamines. Y

The agents may be added to the rubber mix singlyor in combination. In the latter case it is convenient to use the agents as a preformed mixture and such-.pre-formed mixtures of mercaptoarimidazole, Ephenol containing. at

least one tertiary alkyl or alkylcycloalkyl radical having. from 4 to 8 carbon atoms and, optionally, copper-sequestering agent form a furtherfeature of this invention.

The invention is illustrated bu t not' limited by the following examples, in which parts and percentages'ar e by weight.

Example 1 Y Vulcanisable rubber compounds were made up'by the conventional methods according to the following formulae in which the parts are by weight.

Pale crepe rubb Copper sterate Diohenyl guanidine bisl'2-hydroxy-3-tert.- tyl methyl phonyH-methane. bis[2-hydroxy-3-(a-methylcyclohexyl)-fi-methylphenyl] methane 2 1 bis(2-hydroxy-3-tert.-bntyl-5- v 1 ethylphenyy 2-mercaptobenzimidazole 1 1 9. 1m Juneau-110 Mix f.-. 'A '13 o D' g E r' Time in hours to attain Ozp uptake Example 2 Vulcanisableirubber compounds were made up by the conventional methods according to the following formulae 1n Wl'llCl'l the parts are byrwelght.

M G H J -K 100 1 00. 100 100 10 10 1O 10 75 75 75 I 3 3 3 .3 0.2 "0.2 "0.2 0.2 0:5 0.5 0.5 "0:5 di 2 1 v M J inhn'nnl 2 l 1 2-merc5pfn'hen7in mm 1 1 3 The mixes were vulcanised in sheets not" greater than 0.8 mm. thick for 150 minutes at 141 C. and the antioxidant elfect was measured as in Example 1.

I 4 Example 5 The following tional manner:

mixes were prepared in the conven- 5 Mir G. H .T K Mix s T'UVWXYZ Timelnhoursto attain 0.41mi... of: Palecrepe rubber 100 100 100 100 100 100 100 100 0.5 12i;0' 12.5 22.2 Zinc oxide 10 10 10 10 10 10 10 38.6 24.0 40.0 Blane fixe 75 75 75 75 75 75 75- 75 7 10 Stearic acid. 1 l 1 1 l 1 1 1 Sulphur 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Diphenylguanidine 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Example 3 Copperstearate 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

biS[](2-h1y%r0XlI)-35(a-mfitli- 1 1 ycycoexy --rnety- Thefollowmg compounds were prepared 1n the con phenymmethaue 2 1 ventional manner: 2:5-tert.-butyl-4-methyl- 5 penoL; 2 1

M bls(2-hydroxy-3-tert.-butyl-5-methylpheuyl) Mix n... L M N O P methane 2 1 2(a-netbylcycloiexyl) -6- di'nethylpuenol 2 l Palebrene-rubberi.-- Y 100 100 100 100 100 Z-mercaptobeuzimidazole 1 1 1 1 Zinc oxide 10, 10 10 10 10 Blane axe; 75' 75 75 75 75 i tgiii uixi 1( 10 1( 1( 15' I he mixes were vulcanised for 75 minutes at 141 C. Sulphur 2.0 2.0 2.0 2.0 2.0 and tested by the bomb ageing method described in Zlnc diethy 0.375 0.375 0.375 0.375 0.375 Exam 1e 3 Copper stearat 0.2 0.2 0.2 0.2 0.2 p bis[2-hydroxy3 cyclohexyDe-met'hylphenyl1methaue 2 1 1 1 0.95 Mix S T U V W X Y Z Z-mercaptobenzimldazole. 1 9 0. 9 0.95 ethylene-bis(iminodiacetic acid). 0. t-5Q% period in disallcylal ethylene diamlne; 0: days 2.5 8.5 1.0 5.2 4.5 13.5 1.5 5.7 disodium salt otethylene- H bls(imlnodiacetic acid). 0.1 I

' What we claim is: 1. Process for protecting natural rubber against dete- O CThese mixes were vulcanised for 12 minutes at 125 Mormon-by oxidation in the presence. of a member selected from the group consisting of copper and manga- The imtloxldant effect. was measured deter,mmmg nese, which comprises incorporating into the rubber, the tensile strengths of ring-shaped test pieces WhlCh had before curing I been aged for varying periods in an oxygen bomb under 300 psi. oxygen pressure at 70 C.; curves were drawn (a) A sulfur compound, selected from the group coni for each mix, of tensile strength against duration of sisting of Z-rnercaptobenzimidazole, zinc, calcium, and ageing and from the curves WBS lIltlPOlfitBd the time in 40 magnesium salts of 2-mercaptobenzimidazolc, and 2,2- days for'the'tensilestrength to fall to of the una'ged v dibenzimidazyl disulfide; and sample. ([1) A phenol having a substituent selected from'the The following results were obt'arnedz group consisting of tertiary alkyl radicals having'from a 4 to-S'c'arbon atoms and a-methylcyclohexyl.

Mix L 'M' N' 0' F ii 2. The process of claim 1, wherein'said sulfur'eom- 4 pound is Z-mercaptobenzimidazole. v t-50%"period in days; 8.4 14.5 15.0 12.5 15.4 3. The process of claim 1, wherein the proportion of said sulfur compound is from 50% to 200% of the weight of said phenol. Example 4 50 4. The process of claim 3, wherein th'eproporti'on'of Theifollowingmixes were prepared 1111116 conventional said sulfur compound is about 100% of the weight of manner: said phenol.

5. The process of claim 1, wherein the combined amount of '(a) and (b) isfrom about 0.5% to about Me 9 E 4.0% by weight of the rubber. I

6. Process for protecting natural rubber against degggfg z 98 terioration by oxidation, in the presence of a member Blane fixefin 75 7.; selected from the group-consisting of copper and mangaggigg fi 10 nese, wh ch comprises incorporation into the-rubber, be- Su1phur 2.5 2.5 fore cur1ng,- Z-mercaptobeuzthiazole 0. 5 0. 5 I I g gg 2 1 (a) A sulfur compound, selected from'the group cona I 2-mercaptobonriri1iria nln .09 slstlng of a Z-mercaptobenzrmrdazole, z nc, calclum, gggggfig gig tf f fjfjfjf Q2 8:; and magnesium salts of Z-mercaptobenzimidazole, and

.. 2,2'-diben z'irnidazyl disulfide; i

(b) A phenol having a substituent selected from the group These mixes were vulcanised at 141 C. and the .antin le ternary f Y from H 8 oxidant efiect was measured as in Example '3. Carbon atoms and y cyc exy The-following results-Were Obtained! wherein-the combined amount of (a) and (11) is'from p p about"0.5%' to 4% by weight of the rubber; and M" 1. (0 A copper-sequestering agent in an amount of from i about 3% to 10% by'weight'of the combined weight t-50%periodlndays I 11.6 15.5 of and (C)- 7.'The process of claim 6, wherein said copper sequestering agent is selected from the group consisting of 8-hydroxy-quinoline, p-aminophenol, ethylene diamine tetracetic acid, alkali metal salts of ethylene diamine tetracetic acid, and disalicylal ethylene diamine.

8. The process of claim 6, wherein said copper sequestering agent is S-hydroxyquinoline.

9. The process of claim 6, wherein said copper sequestering agent is p-aminophenol.

10. The process of claim 6, wherein said copper sequestering agent is ethylene diamine tetracetic acid.

11. The process of claim 6, wherein said copper sequestering agent is an alkali metal salt of ethylene diamine tetracetic acid.

12. The process of claim 6, wherein said cooper sequestering agent is disalicylal ethylene diamine.

13. A composition of natural rubber protected against oxidative deterioration which consists essentially of natural rubber, a member selected from the group consisting of copper and manganese, a sulfur compound selected from the group consisting of 2-mercaptobenzimidazole, zinc, calcium, and magnesium salts of Z-mercaptobenzimidazole and 2,2-dibenzimidazyl disulfide, and a phenol having a substituent selected from the group consisting of tertiary alkyl radicals having from 4 to 8 carbon atoms and u-rnethylcyclohexyl.

14. A composition according to claim 13, and which also contains a copper sequestering agent.

15. The composition of claim 14, wherein said copper sequestering agent is selected from the group consisting of 8-hydroxyquinoline, p-aminophenol, ethylene diamine 3o tetracetic acid, alkali metal salts of ethylene diamine tetracetic acid, and disalicylal ethylene diamine.

16. The composition of claim 15 wherein the combined amount present of said sulfur compound, said phenol and said copper-sequestering agent is from about 0.5% to about 4.0% by weight of the rubber of which combined amount 3% to 10% is the copper sequestering agent, and the proportion of said sulfur compound is from about to about 200% of the weight of said phenol.

17. The composition of claim 15, wherein said copper sequestering agent is S-hydroxyquinoline.

18. The composition of claim 15, wherein said copper sequestering agent is p-aminophenol.

19. The composition of claim 15, wherein said copper sequestering agent is ethylene diamine tetracetic acid.

20. The composition of claim 15, wherein said copper sequestering agent is an alkali metal salt of ethylene diamine tetracetic acid.

21. The composition of claim 15, wherein said copper sequestering agent is disalicylal ethylene diamine.

References Cited in the file of this patent UNITED STATES PATENTS 2,538,355 Davis et al. Ian. 16, 1951 2,560,028 Kitchen et al. July 10, 1951 2,560,744 Rhines July 17, 1951 2,727,014 Harbison Dec. 13, 1955 

1. PROCESS FOR PROTECTING NATURAL RUBBER AGAINST DETERIORATION BY OXIDATION, IN THE PRESENCE OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF COPPER AND MANGANESE, WHICH COMPRISES INCORPORATING INTO THE RUBBER, BEFORE CURING, (A) A SULFUR COMPOUND, SELECTED FROM THE GROUP CONSISTING OF 2-MERCAPTOBENZIMIDAZOLE, ZINC, CALCIUM, AND MAGNESIUM SALTS OF 2-MERCAPTOBENZIMIDAZOLE, AND 2,2''DIBENZIMIDAZYL DISULFIDE, AND (B) A PHENOL HAVING A SUBSTITUENT SELECTED FROM THE GROUP CONSISTING OF TERTIARY ALKYL RADICALS HAVING FROM 4 TO 8 CARBON ATOMS AND A-METHYLCYCLOHEXYL. 